When adding door architrave to a standard door size you need 2 upright legs which usually measures at 2440mm and 1 head at 1220mm. However, this will depend on what size door you have, to be sure you will need to measure by holding the architrave length against the left hand side of the door using the margins as a guide. Where the margin at the top of the door meets the piece you’re holding is where you mark the architrave.